The present invention relates to a rolling bearing with solid lubricant suitable for use particularly in semiconductor producing apparatuses.
Rolling bearings used in semiconductor producing apparatuses are operated in vacuum requiring a high degree of cleanliness, and hence for lubrication thereof, solid lubricants including laminar materials such as molybdenum disulfide, soft metals such as gold, silver and lead, and high polymers such as PTFE and polyimide are in general use.
Recently, in the semiconductors production field, as the degree of integration of semiconductors increases, the line width of electric circuits has been decreasing. And since it is feared that particles of a solid lubricant occurred from the bearing may adhere to the patterns to short the electric circuits, solid lubricants of soft metal type tend to be hardly employed because of those electrical conductivity. On the other hand, such solid lubricants as molybdenum disulfide and PTFE, though having no electrical conductivity, have little re-adherebility and low resistance; thus, they are inferior in durability to soft metals. Further, recent semiconductor producing apparatus requires not only a bearing which can be used in vacuum but also a bearing which can be used in both air and vacuum and which produces little dust and has corrosion resistance.
More particularly, it is mainly in the wafer treating process that vacuum bearings are used in the semiconductor producing process. And the apparatus used in this process tends to be made an in-line form for purpose of increasing productivity, and the wafer transporting system requires a bearing which can be operated in both air and vacuum. Further, the increased degree of integration of semiconductors necessarily requires to suppress dust discharged from the apparatus. Further, corrosion resistance and heat resistance are also required depending upon locations where bearings are used.
With the above in mind, the present applicant has already applied for patent (Japanese Patent Application No. 190150/1991) on a rolling bearing formed with a solid lubricating film made of polytetrafluoroethylene whose weight average molecular weight is not more than 5,000 (hereinafter referred to as PTFE (A) for brevity's sake).
PTFE heretofore used as a solid lubricant for rolling bearings has a weight average molecular weight of 1.times.105 or above, particularly 1.times.106-1.times.107, but PTFE (A) has a remarkably low shear strength and soft, as compared with the heretofore used PTFE. For this reason, particles of PTFE (A) are superior in re-adherebility, entering any shallow dimples in the mating surface to act as lubricating powder to form a lubricating film and hence they hardly scatter. Further, since the shearing strength is low, the friction coefficient is low, developing superior lubrication performance. In the proceding patent application, PTFE (A) is used to form solid lubricating films on those portions of a rolling bearing which are subject to rolling friction or sliding friction, so that, as compared with the use of other solid lubricants, the durability and low dust production rate are greatly improved, meeting the requirement for high integration and in-line form in the recent semiconductor producing apparatus.
An object of the present invention is to further improve the low dust production rate of said rolling bearing with solid lubricant.